1. Field of the Invention
This invention relates to a partially hydrogenated polymer having acid labile groups of at least one type in which some of the phenolic hydroxyl groups and/or alcoholic hydroxyl groups are crosslinked with a crosslinking group having a C--O--C linkage within a molecule and/or between molecules. It also relates to a chemically amplified positive resist composition comprising the polymer as a base resin which has a high alkali dissolution contrast before and after exposure, high sensitivity and high resolution and is thus suitable as a fine pattern forming material for use in the manufacture of ultra-LSIs.
2. Prior Art
As the LSI technology tends toward higher integration and higher speed, further refinement of pattern rules is required. Under such circumstances, deep-ultraviolet lithography is regarded promising as the next generation of fine patterning technology. The deep-UV lithography is capable of working on the order of 0.5 .mu.m or less and makes it possible to form a resist pattern having a side wall nearly perpendicular to the substrate if a less light absorbing resist material is used.
A number of chemically amplified positive working resist materials using acid catalysts were recently developed as disclosed in JP-B 27660/1990, JP-A 27829/1988, U.S. Pat. Nos. 4,491,628 and 5,310,619. They utilize a high illuminance KrF excimer laser as a deep-UV light source. Since these materials have high sensitivity, resolution and dry etching resistance, they are promising as resist materials especially suited for deep-UV lithography.
The chemically amplified, positive resist materials being known include those of the two-component system comprising a base resin and a photoacid generator and those of the three-component system comprising a base resin, a photoacid generator, and a dissolution inhibitor having an acid labile group.
JP-A 115440/1987 discloses a resist composition comprising poly-4-butoxystyrene and a photoacid generator. Similarly, JP-A 223858/1991 discloses a two-component system resist composition comprising a resin having a tert-butoxy group in its molecule and a photoacid generator and JP-A 211258/1992 discloses a two-component system resist composition comprising a polyhydroxystyrene containing a methyl, isopropyl, tert-butyl, tetrahydro-pyranyl or trimethylsilyl group in its molecule and a photoacid generator.
Furthermore, JP-A 100488/1994 proposes a resist composition comprising a polyhydroxystyrene derivative such as poly[3,4-bis(2-tetrahydropyranyloxy)styrene], poly[3,4-bis(tert-butoxycarbonyloxy)styrene], and poly[3,5-bis (2-tetrahydropyranyloxy)styrene] and a photoacid generator.
The base resins used in these resist compositions have an acid labile group in a side chain. If the acid labile group is a strong acid-decomposable one such as tert-butyl and tert-butoxycarbonyl group, the acid labile group is deactivated through reaction with air-borne basic compounds and becomes unlikely to decompose. Such a resist composition tends to form a pattern having a T-top profile. On the other hand, if the acid labile group is an alkoxyalkyl group such as ethoxyethyl which is decomposable with weak acid, the resist composition is little affected by air-borne basic compounds, but forms a pattern which will become extremely thin with the lapse of time from exposure to heat treatment. The inclusion of a bulky group in a side chain can detract from heat resistance. The composition is less satisfactory in sensitivity and resolution.
Also, polyvinylphenol resins have been widely used as the base resin although resist films thereof are not satisfactorily transparent to deep UV radiation. Since deep UV radiation is not transmitted to the interface between the resist film and the substrate, the dissolution of the resist film in a developer solution becomes uneven in a film thickness direction, resulting in poorly configured resist patterns. No polyvinylphenol resin bases resist materials have reached the practically acceptable level.
In this connection, it is known from JP-A 127386/1993 and 253533/1996 to use a hydrogenated polyvinylphenol derivative as the base resin for the purpose of improving transmittance. Although this approach is successful in improving the pattern configuration to some extent, further improvements in resolution and heat resistance are desired in order to meet the enhanced demand for modern resists.
JP-A 253534/1996 discloses a crosslinked polymer which is suitable as a binder for DUV resist materials having processing stability, high contrast, and good resolution. A by-product is formed as a result of elimination of an acid labile group from the polymer. The by-product can be attached to the base resin again to reduce the differential dissolution rate and hence, the contrast and also causes the exposed region to be partially left undissolved after development, causing scum to generate. The desired resolution enhancement is nut fully accomplished. Further, since both an acetal or ketal group and a crosslinking group are attached to the base resin with an identical reagent, molecular weight control is difficult. Since the choice of the acetal or ketal group and the crosslinking group is constrained, the problem of heat resistance is not fully solved. With these and other problems unsolved, none of the resist compositions thus far proposed are practically satisfactory. There is a desire to overcome these problems.